where M is the continuity constant of F(·), α and γ coercivity and continuity constants of a(·,·) respectively. In practice, these inequalities can be meaningless when the constants involved are large. In particular if γ ≫ α the second inequality is an effective bound for the error only if \(\mathop {\inf }\limits_{{v_h} \in {V_h}} {\left\| {u - {v_h}} \right\|_{{H^1}(\Omega )}}\) is small. For a finite element discretization, this corresponds to a small value of the mesh size h. The associated discretized problem can be therefore computationally expensive or even not affordable.